The present invention relates to direct current dynamoelectric machines, and more particularly to a homopolar machine with circumferentially-segmented magnets.
Homopolar machines in which rotor conductors pass continuously through a unidirectional or unipolar magnetic field are well known. These machines are capable of producing relatively high power outputs with good efficiency, but the known types of homopolar machines require very strong magnetic fields and are inherently low-voltage, high-current machines. The high current outputs of these machines result in difficult current collection problems requiring complicated and expensive arrangements of slip rings with many brushes, or liquid metal current-collecting schemes which involve the use of potentially dangerous materials, such as sodium-potassium alloys. For these reasons, homopolar machines have not been used extensively and have been considered suitable only for certain special applications.
It has been proposed in Mole U.S. Pat. No. 4,041,337 to overcome some of these problems of conventional homopolar machines by providing an axially-segmented magnet machine. In this machine, the magnetic field is divided into segments along the axis of the machine with corresponding axially-spaced rotor segments which may be series-connected to obtain the desired output voltage. Such a machine, especially if superconducting field magnets are used, is capable of relatively high output for a machine of given size but it has certain undesirable limitations. The type of flux path utilized, extending axially through the rotor, results in geometric limitations on the size of the machine, or on the size of each of the axial modules, while the size and losses of the current-collection system required impose severe limitations on the design of the machine as well as requiring liquid metal current-collection systems in most cases, with the attendant complication and risks.